Digital subscriber line (DSL) technology, often referred to as “broadband”, is a family of services that provides high speed digital data transmission over the metallic twisted copper pairs that form part of a local telephone network. DSL is commonly used to provide a customer's home with a network connection, typically to the Internet via an ISP.
Broadband lines are prone to faults. These result in slow line speeds or line drop outs, affecting a customer's service. Some of these faults are easily identified and rectified, such as missing micro-filters in the customer's home. Others are more complex, such as when a line is suffering from degradations in the copper pair at joints between wires or in the insulation surrounding the wires. Various techniques have been developed to help identify such faults.
One known method is to employ metallic line tests, where line test equipment at the telephone exchange runs various line tests. These are typically electrical tests, and the resulting measurements, such as resistance, capacitance and so on, are used to look for various line conditions on the metallic path. Such tests are intended to identify PSTN faults, and can lack sensitivity to fault conditions that affect broadband. Indeed, some of the testing will mask certain faults, as in certain situations the test itself can clear the fault condition as a result of the voltages being applied to the lines. Such testing also requires that specialist test equipment be connected to the line, requiring PSTN and DSL services to be temporarily disabled whilst the testing takes place. The test equipment typically requires some sort of relay to switch in and those relays tend to have a limited lifespan.
Other methods similarly employ specialist test equipment, for example interacting with the training tones from the customer premises equipment (the DSL modem).